I am using 3 freetronics shift register expansion modules to try and run 24 LED's that flash on and off to the beat of music. I have little programming experience and have a week before handing this in. Can someone please help me to do the programming? I have been trying to program with little success.

Id suggest getting a msgeq7 for splitting the audio into channels, then just mapping that to your leds,id suggest using spi with those shift registers to keep it changing as fast as possible to make it look good

I don't believe you'd need an arduino at all for this, let alone your shift registers. You could use a voltage divider setup with a bunch of comparators, each one's output driving one LED, which would give you a rudimentary volume display--more LEDs lit means higher volume. Just put them in a line like a bar graph!